To correlate other fertility signs such as cervical mucus or cervical position with actual ovulation on a

BBT chart (see Other Signs below)

To calculate the follicular and the corpus luteum phases (a key to possible infertility issues)

More about this last point: A biphasic curve has two phases: before and after ovulation. Charting not only helps you plot the biphasic curve, but you can measure the length of the two phases as well. If the second phase is too short (less than 12 days), this can cause problems with implantation of fertilized eggs. Fertility charting can help reveal such an issue.